1. Field of the Invention
The present invention relates generally to an apparatus and method for detecting a crack.
2. Description of the Related Art
If the heat exchangers such as a condenser, conductor and steam generator of a nuclear power plant, the barrel of a gun, an oil pipeline, or the like is damaged because of the corrosion, fatigue or crack of its piping system, a very serious accident may occur. In order to prevent such accidents, apparatuses for detecting a crack in a small-bore piping system, such as an eddy current testing (ECT) apparatus, have been developed.
Conventional apparatuses for detecting a crack in a small-bore piping system chiefly use a pickup coil or a pancake coil.
A detection apparatus using a pickup coil functions to allow the pickup coil to be inserted into a small-bore piping system, apply an alternating current (AC) current to an input coil side, measure a current induced on an output coil side, and then detect a crack. This detection apparatus is disadvantageous in that it is difficult to detect a small crack because the size of its sensor is large, and it is also difficult to estimate the shape or size of a crack.
A detection apparatus using a pancake coil functions to allow a small pancake-type coil to be inserted into a piping system, move the coil in the axial direction of the piping system while rotating the coil, and then measure a change in induced current inside the piping system in two dimensions. While this detection apparatus is advantageous in that it can measure a small crack and measure the shape and size of a crack, it is disadvantageous in that a scanner is required, a long time is required to perform measurement and the size of a sensor is limited.